The present invention generally relates to a new hydrogenated oxidized silicon carbon (SiCOH) low dielectric constant material which is thermally stable to at least 350xc2x0 C. and a method for fabricating films of this material and electronic devices containing such films and more particularly, relates to a low dielectric constant, thermally stable hydrogenated oxidized silicon carbon (SiCOH) film for use as an intralevel or interlevel dielectric, cap material, or hard mask/polish stop in a ULSI back-end-of-the-line (BEOL) wiring structure, electronic structures containing the films and a method for fabrication such films and structures.
The continuous shrinking in dimensions of electronic devices utilized in ULSI circuits in recent years has resulted in increasing the resistance of the BEOL metalization as well as increasing the capacitance of the intralayer and interlayer. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (k) insulators and particularly those with k significantly lower than that of silicon oxide are needed to reduce the capacitances. Dielectric materials that have low k values have been commercially available, for instance, one of such materials is polytetrafluoroethylene (PTFE) with a k value of 2.0. However, these dielectric materials are not thermally stable when exposed to temperatures above 300xcx9c350xc2x0 C. which renders them useless during integration of these dielectrics in ULSI chips which require a thermal stability of at least 400xc2x0 C.
The low-k materials that have been considered for applications in ULSI devices include polymers containing Si, C, O, such as methylsiloxane, methylsesquioxanes, and other organic and inorganic polymers. For instance, materials described in a paper xe2x80x9cProperties of new low dielectric constant spin-on silicon oxide based dielectricsxe2x80x9d by N. Hacker et al., published in Mat. Res. Soc. Symp. Proc., vol. 476 (1997) p25 appear to satisfy the thermal stability requirement, even though some of these materials propagate cracks easily when reaching thicknesses needed for integration in the interconnect structure when films are prepared by a spin-on technique. Furthermore, the precursor materials are high cost and prohibitive for use in mass production. In contrast to this, most of the fabrication steps of VLSI and ULSI chips are carried out by plasma enhanced chemical or physical vapor deposition techniques. The ability to fabricate a low-k material by a PECVD technique using readily available processing equipment will thus simplify its integration in the manufacturing process and create less hazardous waste.
It is therefore an object of the present invention to provide a low dielectric constant material of hydrogenated oxidized silicon carbon which is thermally stable to at least 350xc2x0 C. and exhibits very low crack propagation.
It is another object of the present invention to provide a method for fabricating a low dielectric constant and thermally stable hydrogenated oxidized silicon carbon film.
It is a further object of the present invention to provide a method for fabricating a low dielectric constant, thermally stable hydrogenated oxidized silicon carbon film from a precursor which contains Si, C, O and H and which may have a ring structure.
It is another further object of the present invention to provide a method for fabricating a low dielectric constant, thermally stable hydrogenated oxidized silicon carbon film from a precursor mixture which contains atoms of Si, C, O, and H.
It is still another further object of the present invention to provide a method for fabricating a low dielectric constant, thermally stable hydrogenated oxidized silicon carbon film in a parallel plate plasma enhanced chemical vapor deposition chamber.
It is yet another object of the present invention to provide a method for fabricating a low dielectric constant, thermally stable hydrogenated oxidized silicon carbon film for use in electronic structures as an intralevel or interlevel dielectric in a BEOL interconnect structure.
It is still another further object of the present invention to provide a method for fabricating a thermally stable hydrogenated oxidized silicon carbon film of low dielectric constant capable of surviving a process temperature of at least 350xc2x0 C. for four hours.
It is yet another further object of the present invention to provide a low dielectric constant, thermally stable hydrogenated oxidized silicon carbon film that has low internal stresses and a dielectric constant of not higher than 3.6.
It is still another further object of the present invention to provide an electronic structure incorporating layers of insulating materials as intralevel or interlevel dielectrics in a BEOL wiring structure in which at least one of the layers of insulating materials comprise hydrogenated oxidized silicon carbon films.
It is yet another further object of the present invention to provide an electronic structure which has layers of hydrogenated oxidized silicon carbon films as intralevel or interlevel dielectrics in a BEOL wiring structure which contains at least one dielectric cap layer formed of different materials for use as a reactive ion etching mask, a polish stop or a diffusion barrier.
It is still another further object of the present invention to provide an electronic structure with intralevel or interlevel dielectrics in a BEOL wiring structure which has at least one layer of hydrogenated oxidized silicon carbon films as reactive ion etching mask, a polish stop or a diffusion barrier.
In accordance with the present invention, a novel hydrogenated oxidized silicon carbon (SiCOH) low dielectric constant material that is thermally stable to at least 350xc2x0 C. is provided. The present invention further provides a method for fabricating a thermally stable, low dielectric constant hydrogenated oxidized silicon carbon film by reacting a precursor gas containing atoms of Si, C, O, and H in a parallel plate plasma enhanced chemical vapor deposition chamber. The present invention still further provides an electronic structure that has layers of insulating materials as intralevel or interlevel dielectrics used in a BEOL wiring structure wherein the insulating material can be a hydrogenated oxidized silicon carbon film.
In a preferred embodiment, a method for fabricating a thermally stable hydrogenated oxidized silicon carbon film can be carried out by the operating steps of first providing a parallel plate plasma enhanced chemical vapor deposition chamber, positioning an electronic structure in the chamber, flowing a precursor gas containing atoms of Si, C, O, and H into the chamber, depositing a hydrogenated oxidized silicon carbon film on the substrate, and optionally heat treating the film at a temperature not less than 300xc2x0 C. for a time period of at least 0.5 hour. The method may further include the step of providing a parallel plate reactor which has a conductive area of a substrate chuck between about 300 cm2 and about 700 cm2, and a gap between the substrate and a top electrode between about 1 cm and about 10 cm. A RF power is applied to one of the electrodes at a frequency between about 12 MHZ and about 15 MHZ. The substrate may be positioned on the powered electrode or on the grounded electrode. An optional heat treating step may further be conducted at a temperature not higher than 300xc2x0 C. for a first time period and then at a temperature not lower than 380xc2x0 C. for a second time period, the second time period is longer than the first time period. The second time period may be at least 10 folds of the first time period.
The precursor utilized can be selected from molecules with ring structures such as 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS, or C4H16O4Si4), tetraethylcyclotetrasiloxane (C8H24O4Si4), or decamethylcyclopentasiloxane (C10H30O5Si5). However, other precursors comprising Si, C, O, and H containing gases may also be used. Such precursors may be selected from the group of methylsilanes, such as tetramethylsilane (Si(CH3)4) or trimethylsilane (SiH(CH3)3)), with or without the addition of oxygen to the feed gas. The precursor can be delivered directly as a gas to the reactor delivered as a liquid vaporized directly within the reactor, or transported by an inert carrier gas such as helium or argon. The precursor mixture may further contain elements such as nitrogen, fluorine or germanium.
The deposition step for the hydrogenated oxidized silicon carbon low dielectric constant film may further include the steps of setting the substrate temperature at between about 25xc2x0 C. and about 400xc2x0 C., setting the RF power density at between about 0.02 W/cm2 and about 1.0 W/cm2, setting the precursor flow rate at between about 5 sccm and about 200 sccm, setting the chamber pressure at between about 50 mTorr and about 3 Torr, and setting a substrate DC bias at between about 0 VDC and about xe2x88x92400 VDC. The deposition process can be conducted in a parallel plate type plasma enhanced chemical vapor deposition chamber.
The present invention is further directed to an electronic structure which has layers of insulating materials as intralevel or interlevel dielectrics in a BEOL interconnect structure which includes a pre-processed semiconducting substrate that has a first region of metal embedded in a first layer of insulating material, a first region of conductor embedded in a second layer of insulating material which comprises SiCOH, said second layer of insulating material being in intimate contact with said first layer of insulating material, said first region of conductor being in electrical communication with said first region of metal, and a second region of conductor being in electrical communication with said first region of conductor and being embedded in a third layer of insulating material comprises SiCOH, said third layer of insulating material being in intimate contact with said second layer of insulating material. The electronic structure may further include a dielectric cap layer situated in-between the first layer of insulating material and the second layer of insulating material, and may further include a dielectric cap layer situated in-between the second layer of to insulating material and the third layer of insulating material. The electronic structure may further include a first dielectric cap layer between the second layer of insulating material and the third layer of insulating material, and a second dielectric cap layer on top of the third layer of insulating material.
The dielectric cap material can be selected from silicon oxide, silicon nitride, silicon oxinitride, refractory metal silicon nitride with the refractory metal being Ta, Zr, Hf or W, silicon carbide, silicon carbo-oxide, and their hydrogenated compounds. The first and the second dielectric cap layer may be selected from the same group of dielectric materials. The first layer of insulating material may be silicon oxide or silicon nitride or doped varieties of these materials, such as PSG or BPSG. The electronic structure may further include a diffusion barrier layer of a dielectric material deposited on at least one of the second and third layer of insulating material. The electronic structure may further include a dielectric layer on top of the second layer of insulating material for use as a RIE hard mask/polish stop layer and a dielectric diffusion barrier layer on top of the dielectric RIE hard mask/polish-stop layer. The electronic structure may further include a first dielectric RIE hard mask/polish-stop layer on top of the second layer of insulating material, a first dielectric RIE diffusion barrier layer on top of the first dielectric polish-stop layer, a second dielectric RIE hard mask/polish-stop layer on top of the third layer of insulating material, and a second dielectric diffusion barrier layer on top of the second dielectric polish-stop layer. The electronic structure may further include a dielectric cap layer of same materials as mentioned above between an interlevel dielectric of SiCOH and an intralevel dielectric of SiCOH.